Ceramic powder and multi-layer ceramic capacitor

ABSTRACT

A multi-layer ceramic capacitor is made by alternately layering a dielectric layer constituted by a sintered body of a ceramic powder, and an internal electrode layer. The ceramic powder contains barium titanate powder having a perovskite structure with a median size of 200 nm or smaller as measured by SEM observation, wherein the barium titanate powder is such that the percentage of barium titanate particles having twin defects in the barium titanate powder is 13% or more as measured by TEM observation and that its crystal lattice c/a is 1.0080 or more. The ceramic powder has a wide range of optimum sintering temperatures and thus offers excellent productivity and is particularly useful in the formation of thin dielectric layers of 1 μm or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/849,367, filed Mar. 22, 2013, which claims priority to JapanesePatent Application No. 2012-080787, filed Mar. 30, 2012, each disclosureof which is herein incorporated by reference in its entirety. Theapplicant herein explicitly rescinds and retracts any prior disclaimersor disavowals made in any parent, child or related prosecution historywith regard to any subject matter supported by the present application.

BACKGROUND

Field of the Invention

The present invention relates to a ceramic powder that contains bariumtitanate having a perovskite structure, and a multi-layer ceramiccapacitor (MLCC) obtained by using said ceramic powder, particularlyuseful for a MLCC using a thin-layer dielectric layer.

Description of the Related Art

Multi-layer ceramic capacitors (MLCCs) are used in various electronicdevices including mobile devices and communications devices.

The trend for smaller, higher-performance MLCCs and other electroniccomponents has been prominent in recent years and, in the case of MLCCs,for example, these capacitors are becoming significantly smaller andlarger in capacity. The capacity of a MLCC is proportional to the numberof dielectric layers constituting the base material of the MLCC, andinversely proportional to the thickness per dielectric layer, andconsequently it is desirable to keep the dielectric layer thin, such as1 μm or less, and increase the number of layers.

For the material ceramic powder with which to form such dielectriclayer, barium titanate powder having a perovskite structure is widelyused.

To ensure performance and reliability, and also from the viewpoint ofphysical characteristics, it is important that the barium titanatepowder consist of fine particles so as to make the aforementioneddielectric layer thinner.

Here, one proposed method to synthesize a barium titanate compoundsuitable for making the dielectric layer thinner is to crush and mixwith an organic solvent a powder mixture containing barium carbonatepowder and titanium dioxide powder, and then sinter the crushed andmixed powder mixture to obtain a powder of barium titanate compound(Patent Literature 1).

According to Patent Literature 1, the powder of barium titanate compoundobtained by the method described therein has an average particle size of100 nm or smaller, contains twin defects in at least 10% of theparticles, and its standard deviation of particle distribution is 20 orsmaller. It is also described that, by using this powder, variation ofsurface roughness can be suppressed and consequently the shorting rateand insulation resistance failure of the MLCC can be suppressed.

BACKGROUND ART LITERATURE Patent Literature

-   [Patent Literature 1] Japanese Patent Laid-open No. 2011-132071

SUMMARY

However, while Patent Literature 1 does not present specific data onelectrical characteristics, such barium titanate ceramic powder with asmall particle size of 100 nm or smaller is generally subject to asignificant variation in the electrical characteristics of the obtaineddielectric layer, relative to changes in the oxygen partial pressure,temperature, and other sintering conditions, for example, when thepowder is sintered and made into the dielectric layer. In other words,the range of optimum sintering temperatures is narrow.

Generally when manufacturing a MLCC, laminates called “green sheets,”each constituted by internal electrode layers and layers containingceramic powder, are stacked and layered on top of one another to createmany MLCC moldings, which are then placed into a sintering furnace andsintered all at once.

For this reason, it is difficult to heat each molding in a completelyuniform manner, and because sintering irregularities occur wherebysintering is promoted more in some parts and suppressed in other parts,a narrow range of optimum sintering temperatures leads to defects andconsequently a lower yield.

Accordingly, the method described in Patent Literature 1 is not expectedto produce a high yield, because changes in the sintering conditions,even minor changes in the temperature or oxygen partial pressure, willsignificantly affect the characteristics of the resulting MLCC and alsoreduce the yield considerably.

Accordingly, an object of the present invention is to provide a ceramicpowder whose main ingredient is barium titanate having a perovskitestructure, wherein said powder has a wide range of optimum sinteringtemperatures and thus offers excellent productivity and is particularlyuseful in the formation of thin dielectric layers of 1 μm or less, sothat highly reliable, uniform MLCC products can be provided at a highyield.

The inventor of the present invention completed the present inventionafter discovering that such problems could be resolved by a ceramicpowder which has a specific average particle size or smaller, exhibitstwin defects by a specific percentage or more, and contains bariumtitanate of high tetragonality whose crystal lattice c/a is at or higherthan a specific value.

In other words, the present invention is a ceramic powder that containsbarium titanate having a perovskite structure, with an average particlesize (median size) of 200 nm or smaller as measured by SEM observation,wherein said ceramic powder is such that the percentage of twin defectsin the barium titanate is 13% or more as measured by TEM observation andthat its crystal lattice c/a is 1.0080 or more.

To obtain an excellent dielectric layer, it is desirable that theaforementioned barium titanate has an average particle size of 80 to 200nm.

Preferably the barium titanate having a perovskite structure toconstitute the ceramic powder proposed by the present invention has apercentage of twin defects of 13 to 23% and a lattice c/a of 1.0091 to1.0105. By using the ceramic powder proposed by the present invention,which meets the above ranges, MLCCs can be produced at a high yield.

Furthermore, the MLCC proposed by the present invention is made byalternately layering a dielectric layer constituted by a sintered bodyof the ceramic powder proposed by the present invention, and an internalelectrode layer.

According to the present invention, a ceramic powder is provided whosemain ingredient is barium titanate having a perovskite structure,wherein said powder has a wide range of optimum sintering temperaturesand thus offers excellent productivity and is useful in the formation ofthin dielectric layers of 1 μm or smaller, and by using this ceramicpowder, MLCCs can be manufactured at a high yield and consequently theMLCC manufacturing cost can be reduced.

Any discussion of problems and solutions involved in the related art hasbeen included in this disclosure solely for the purposes of providing acontext for the present invention, and should not be taken as anadmission that any or all of the discussion were known at the time theinvention was made.

For purposes of summarizing aspects of the invention and the advantagesachieved over the related art, certain objects and advantages of theinvention are described in this disclosure. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings are greatlysimplified for illustrative purposes and are not necessarily to scale.

FIG. 1 is a simple drawing showing a barium titanate particle in whichtwin defects are formed.

FIG. 2 is a schematic longitudinal cross-section view of a multi-layerceramic capacitor conforming to the present invention.

DESCRIPTION OF THE SYMBOLS

-   -   1 Multi-layer ceramic capacitor    -   10 Ceramic sintered body    -   11 Laminate    -   12 Dielectric layer    -   13 Internal electrode layer    -   15 Cover layer    -   20 External electrode

DETAILED DESCRIPTION OF EMBODIMENTS

As mentioned above, the ceramic powder proposed by the present inventioncontains barium titanate having a perovskite structure, and the averageparticle size (median size) of the barium titanate as measured byobservation using a scanning electron microscope (SEM) is 200 nm orsmaller. The particle size can be the maximum width of the particleobserved with SEM. The median size is the particle size of the medianparticle (d50) when counting particles in the order of the size.

The aforementioned average particle size can be obtained by observing apowder sample of barium titanate using a SEM wherein n=500 (measuring500 particles), and then taking the median size of the measuredparticles. The 500 particles can be selected randomly or can be all theparticles observed in a randomly selected region or regions.

If the average particle size is 200 nm or larger, a smooth and highlyreliable dielectric layer of 1 μm or less in thickness cannot beobtained.

Additionally, the average particle size is normally 80 nm or more, orpreferably 80 to 200 nm from the viewpoint of obtaining a thindielectric layer from the ceramic powder proposed by the presentinvention. How to adjust the average particle size will be describedlater.

Next, the aforementioned barium titanate having a perovskite structurehas a percentage of twin defects, as measured by observation using atransmission electron microscope (TEM), of 13% or more. The percentageof twin defects is measured by observing a powder of the barium titanateusing a TEM and counting, among 100 particles (n=100 wherein the 100particles can be selected randomly or can be all the particles observedin a randomly selected region or regions), those particles in which twindefects are formed. FIG. 1 shows a schematic drawing of a bariumtitanate particle in which twin defects are formed (the right particlewith two lines).

Under the present invention, probably the fact that the percentage oftwin defects in the barium titanate having a perovskite structure is 13%or more and that its crystal lattice c/a is at a specific value or moreproduces some kind of synergistic effect and gives a wide range ofoptimum sintering temperatures to the ceramic powder of the presentinvention.

From such viewpoint, preferably the aforementioned percentage of twindefects is 13 to 23%. How to adjust the percentage of twin defects willbe described later.

As mentioned above, the crystal lattice c/a of the barium titanatehaving a perovskite structure is 1.0080 or more. The c/a can be obtainedby measuring the diffraction peak of the barium titanate (as a bariumtitanate powder sample in its entirety) according to any known powderX-ray diffraction method, analyzing the obtained diffraction peakaccording to the Rietveld method, and then calculating the latticeconstants for axis a and axis c.

Such ceramic powder proposed by the present invention, having hightetragonality of barium titanate and a certain percentage or more oftwin defects, has a wide range of optimum sintering temperatures andthis wide sintering temperature range can be used to manufacture MLCCsat a high yield. In this disclosure, the “ceramic powder” contains the“barium titanate powder” as a main or predominant composition, consistsessentially of the “barium titanate powder”, is characterized by the“barium titanate powder”, or is equivalent to the “barium titanatepowder”.

In addition, high tetragonality of barium titanate is desirable becausethe dielectric constant of barium titanate will increase and the MLCCwill have a higher capacity.

From the above viewpoints, preferably the c/a is 1.0091 to 1.0105because, as long as this c/a range is maintained, any capacity variationof the MLCC obtained using the ceramic powder of the present inventionwill remain 2% or less. How to adjust the c/a will be described later.

Next, how to manufacture the ceramic powder proposed by the presentinvention is explained. The manufacturing method is not limited in anyway, so long as the barium titanate constituting the main ingredient ofthe powder meets the various parameters explained above. However, thepowder can be manufactured as described below by considering andadjusting the various conditions and factors, for example.

In general, titanium material and barium material are reacted with eachother to synthesize barium titanate, which is then heat-treated andsintered into a ceramic powder, after which the powder is crushed toadjust the particle size as necessary and, if necessary, the crushedpowder is further mixed with various additive compounds.

Various methods have been known to synthesize the aforementioned bariumtitanate, where examples include the sol-gel method, hydrothermalmethod, and solid phase method.

Among these methods, the sol-gel method and hydrothermal method tend tosuppress generation of twin defects and lower the c/a value.

The solid phase method tends to generate more twin defects and raise thec/a value.

In addition, the c/a value tends to rise if the ratio of barium andtitanium (Ba/Ti) in the synthesized barium titanate is slightly greaterthan the stoichiometric level, or it tends to drop if this ratio islower than the stoichiometric level. This ratio does not affect thepercentage of twin defects much.

Furthermore, under the present invention, preferably the aforementionedheat treatment is implemented in two separate stages of hydrothermaltreatment and heat treatment.

If the temperature or time of the aforementioned heat treatment ishigher or longer, the percentage of twin defect generation increases andthe c/a value tends to rise. Conversely if the temperature or time ofheat treatment is lower or shorter, generation of twin defects issuppressed and the c/a value tends to drop.

The aforementioned hydrothermal treatment is realized by introducinginto water or specified aqueous solution or other liquid the bariumtitanate powder that has been synthesized by the sol-gel method, etc.,and then adding thermal energy to the powder using the liquid as themedium.

Preferably the hydrothermal treatment temperature is 100° C. or higher,because the tetragonality of barium titanate is not expected to increasemuch when this temperature is lower than 100° C. The hydrothermaltreatment temperature is normally 200° C. or lower.

The hydrothermal treatment time is not limited in any way, but at leastone hour of hydrothermal treatment is enough and normally the treatmenttime is 12 hours or less. As for the pressure of hydrothermal treatment,sufficient effects can be expected at a pressure of at least 1 MPa.

In addition, while the liquid for hydrothermal treatment may be water,it is preferable to use an aqueous solution that contains A-site metalions of the aforementioned barium titanate having a perovskitestructure, or specifically barium ions, to a certain concentration, ordesirable to use an aqueous solution that contains A-site metal ions byat least 0.1 times the mole number of A-site metal contained in thepowder to be treated.

After the hydrothermal treatment, the barium titanate powder is driedand then heat-treated to increase the particle size and thereby obtain abarium titanate powder having a desired average particle size. This heattreatment further increases the percentage of twin defects in bariumtitanate and the c/a value of its crystal lattice.

Conditions of the aforementioned heat treatment are not limited in anyway, but the heat treatment, normally, is performed under the conditionsof 500 to 1200° C. for 0.5 to 6 hours, or preferably under theconditions of 890 to 970° C. for 2 to 6 hours. This heat treatment maybe performed in atmosphere or in an ambience of N₂, etc.

By providing heat treatment at a specific temperature for a specifiedtime as mentioned above, the level of particle growth can be controlledand a desired average particle size can be achieved. While the averageparticle size of barium titanate powder is normally 10 to 40 nm beforesintering, this heat treatment (sintering) increases the size normallyto as much as 80 to 200 nm.

The heat treatment explained above increases the percentage of twindefects in barium titanate and raises the c/a value of crystal lattice.

The barium titanate powder thus obtained is crushed to adjust theparticle size, as necessary, or crushing is combined with classificationto regulate the particle size.

This crushing can be done using either a wet method or dry method, butdry crushing is preferred from the viewpoint of drying cohesion. Note,however, that dry crushing tends to lower the c/a value. It does notaffect the percentage of twin defects much.

Under the present invention, individual conditions, etc., areadjusted/set as deemed appropriate, with an understanding of what eachof the above operations tends to do, to manufacture a barium titanatepowder having a perovskite structure and meeting the average particlesize, percentage of twin defects and c/a value as specified under thepresent invention.

Particularly under the present invention, it is preferable to obtain abarium titanate powder by: manufacturing barium titanate according tothe sol-gel method or solid phase method; hydrothermally treating themanufactured barium titanate under the conditions of 110 to 120° C. for2 to 24 hours at a pH of 13.0 to 13.5; heat-treating the hydrothermallytreated barium titanate under the conditions of 890 to 970° C. for 2 to6 hours; and dry-crushing the heat-treated barium titanate as necessary.

The ceramic powder proposed by the present invention contains a bariumtitanate powder obtained in the manner described above, for example, andit also contains various additive compounds as necessary, as describedlater.

For example, the ceramic powder proposed by the present invention, beingobtained as explained above, has a wide range of optimum sinteringtemperatures and a small average particle size, and thesecharacteristics can be used to manufacture, at a high yield,high-quality MLCCs having a dielectric layer of 1 μm or less inthickness. Manufactured MLCCs have sufficient capacitance, present lesscapacitance variation among individual products, and are resistant todefects.

Next, a multi-layer ceramic capacitor according to an embodiment of thepresent invention is explained. FIG. 2 is a schematic longitudinalcross-section view of a multi-layer ceramic capacitor 1 conforming tothe present invention.

The multi-layer ceramic capacitor 1 is generally constituted by aceramic sintered body 10 having standard chip dimensions and shape (suchas a rectangular solid of 1.0×0.5×0.5 mm), and a pair of externalelectrodes 20 formed on both sides of the ceramic sintered body 10. Theceramic sintered body 10, whose main ingredient is barium titanateparticle crystal, has a laminate 11 formed by alternately layeringdielectric layers 12 and internal electrode layers 13 inside, and coverlayers 15 formed as the outermost layers provided at the top and bottomin the laminating direction.

The laminate 11, where each dielectric layer 12 sandwiched by twointernal electrode layers 13 has a thickness of 1 μm or less (such asapprox. 900 nm) according to the specifications of capacitance andrequired pressure resistance, etc., has a high-density, multi-layerstructure comprising several dozen to several hundred layers in total.

The cover layers 15 formed as the outermost layers of the laminate 11protect the dielectric layers 12 and internal electrode layers 13 fromexternal contamination due to humidity, contaminants, etc., and preventdeterioration of these layers over time.

The multi-layer ceramic capacitor 1 is manufactured as follows, forexample. First, a material fine-particle powder whose main ingredient isbarium titanate is wet-mixed with additive compounds, after which themixture is dried and crushed to prepare a dielectric powder (ceramicpowder conforming to the present invention). Examples of the additivecompounds include oxides of Mg, Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,Cr, V, Mn, Co, Ni, Nb, Ta, Mo, W, Si, Li, B, Na and K, among others.These additive compounds, normally, are added by 0.01 to 0.1 mol intotal, per 1 mol of barium titanate.

The prepared dielectric powder is wet-mixed using a binder such aspolyvinyl butyral resin, and an organic solvent such as ethanol, afterwhich the mixture is coated on a base material in a band form as adielectric green sheet of 1 μm or less in thickness according to thedie-coater method, doctor blade method, etc., and then dried. Next, ametal conductive paste containing organic binder is printed on thesurface of the dielectric green sheet by means of screen printing orgravure printing, to place an internal electrode layer 13 pattern. Forthe aforementioned metal, nickel is widely used from the viewpoint ofcost.

It is possible to uniformly disperse barium titanate with an averageparticle size of 50 nm or smaller, in the aforementioned metalconductive paste, as a co-material. Thereafter, a specified number ofdielectric green sheets, which have been stamped out to an identicalsize of 15 cm×15 cm, for example, are layered so that the internalelectrode layers 13 and dielectric layers 12 alternate. Cover sheetsthat will become cover layers 15 are then pressure-bonded at the top andbottom of the layered dielectric green sheets, after which the laminateis cut to specified chip dimensions (such as 1.0 mm×0.5 mm) and then aNi conductive paste that will form external electrodes 20 is coated onboth side faces of the laminate and dried. This way, a molding ofmulti-layer ceramic capacitor 1 is obtained.

The molding of multi-layer ceramic capacitor 1 thus obtained is placedin a N₂ ambience of approx. 350° C. to remove the binder, and thensintered for 10 minutes to 2 hours at 1100 to 1280° C. under a mixed gascontaining N₂, H₂ and H₂O (whose oxygen partial pressure is approx.1.0×10⁻¹¹ MPa), to obtain a multi-layer ceramic capacitor 1.

In the obtained multi-layer ceramic capacitor 1, the internal electrodelayers 13 are embedded in such a way that their edges are exposedalternately at both end faces of the dielectric layers 12 in the lengthdirection, where the exposed edges of internal electrode layers 13 areconnected to the external electrodes 20.

Also, the thickness of the dielectric layer 12 is normally 3 μm or less,or preferably 0.5 to 1 μm, while the thickness of the internal electrodelayer 13 is normally 0.5 to 3 μm. With the ceramic powder proposed bythe present invention, the average particle size of its main ingredient,or specifically barium titanate, is controlled to 200 nm or smaller, andtherefore a surface of excellent smoothness can be achieved even on suchthin dielectric layer and, consequently a multi-layer ceramic capacitorresistant to shorting and other problems can be obtained.

Furthermore, the aforementioned sintering forms particles of thecore-shell structure, where each particle has a core of barium titanatebeing the main ingredient of the aforementioned dielectric powder, and ashell constituted by the aforementioned additive compounds and solidsolution of barium titanate, and this structure adds favorabletemperature characteristics to the dielectric layer and keeps changes incapacitance and other performance-related characteristics to a minimum,even when the MLCC is subject to changing ambient temperatures.

EXAMPLES Example 1

A barium titanate powder having a perovskite structure was obtainedaccording to the method described below.

First, a barium titanate powder of 15 nm in average particle size and1.0021 in Ba/Ti ratio, synthesized by the sol-gel method, washydrothermally treated under the conditions of 120° C. for 6 hours at apH of 13.5, and then heat-treated (sintered) in a N₂ ambience of 970° C.for 2 hours, to obtain a barium titanate powder having a perovskitestructure. The average particle size of the barium titanate was 145 nm,percentage of particles containing twin defects was 16%, and c/a was1.0101.

As for the average particle size, a powder sample was observed using aSEM and sizes of 500 particles were measured, and the median size(diameter) was taken as the average particle size.

The percentage of twin defects was obtained by observing a powder sampleusing a TEM and counting, among 100 particles, those particles in whichtwin defects were formed.

Furthermore, the c/a was obtained by X-ray diffraction measurement ofpowder, followed by the Rietveld analysis.

The obtained barium titanate powder was used as the material to obtain aceramic powder based on a X7R dielectric composition {(100 BaTiO₃-1.0HO₂O₃-1.0 MgO-0.7 MnO₂-1.5 SiO₂); the unit is mol}, after which a MLCCmolding was prepared using a normal method and then sintered in asintering furnace, to prepare a MLCC having 50 dielectric layers, 51nickel internal electrode layers, and thickness per dielectric layer of1 μm.

When one hundred MLCC samples were measured for capacitance to evaluatethe average capacitance and a standard deviation relative to the averagecapacitance, the following results were obtained, suggesting that theobtained MLCCs presented a very uniform capacitance distribution.

[Mathematical Formula 1]Cap=1.08 μF.σ/ X =1.7%

As for the aforementioned standard deviation (variation in capacitance),samples with a standard deviation of less than 3.0% were judgedacceptable because the greater the variation, the lower the yield oncapacitance becomes.

Since the samples presented a small variation in capacitance as isevident above, the ceramic powder proposed by the present inventionprovides a wide range of optimum sintering temperatures and achieveshigh productivity.

The above results are summarized in Tables 1 and 2 below. It should benoted that a TEM analysis of sintered MLCCs found that the measuredMLCCs contained twin defects at a percentage equivalent to thepercentage of twin defects in the material barium titanate powder usedin the manufacture thereof.

Comparative Example 1

When the barium titanate powder having a perovskite structure asobtained in Example 1 was passed through an air jet type dry crusher(Jetmizer) twice, the average particle size of the aforementioned powderbecame 130 nm, while the c/a became 1.0078. The percentage of particlescontaining twin defects remained unchanged at 16% as before thecrushing.

This barium titanate powder was used as the material to obtain a ceramicpowder of the same composition as in Example 1, to create a MLCC having50 dielectric layers, 51 nickel internal electrode layers, and thicknessper dielectric layer of 1 μm. When 100 MLCC samples were evaluated forcapacitance and a standard deviation relative to the averagecapacitance, the following results were obtained, suggesting that theobtained MLCCs had a poor capacitance distribution and large variationin capacitance.Cap=0.98 μF.σ/ X =3.2%  [Mathematical Formula 2]

The above results are summarized in Tables 1 and 2 below. It should benoted that a TEM analysis of sintered MLCCs found that the measuredMLCCs contained twin defects at a percentage equivalent to thepercentage of twin defects in the material ceramic powder used in themanufacture thereof.

Examples 2 to 13, Comparative Examples 2 to 4

Barium titanate powders were manufactured in the same manner as inExample 1, except that the method for synthesizing barium titanate,average particle size before/after heat treatment, Ba/Ti ratio, variousheat treatment conditions, crushing conditions, generation ratio of twindefects, and c/a value, were changed as shown in Table 1 below.

The obtained barium titanate powder was used as the material to preparea ceramic powder of the same composition as in Example 1, after which aMLCC molding was created according to a normal method and then sinteredin a sintering furnace, to prepare a MLCC having 51 nickel internalelectrode layers and a thickness of 1 μm per dielectric layer. Onehundred MLCC samples were measured to evaluate the capacitance and astandard deviation relative to the average capacitance.

The results are shown in Table 2 below. It should be noted that, in allexamples, a TEM analysis of sintered MLCCs found that the measured MLCCscontained twin defects at a percentage equivalent to the percentage oftwin defects in the material ceramic powder used in the manufacturethereof.

TABLE 1 BaTiO₃ material Average Percentage Average Treatment [1]Treatment [2] particle of twin particle Method of Hydrothermal Heat Drysize defects size synthesis Ba/Ti treatment treatment crushing nm % c/aExample [1] 15 nm Sol-gel 1.0021 120° C./ 970° C./ None 145 16% 1.0101method 6 hours/ 2 hours/ pH of 13.5 N₂ ambience Example [2] 15 nmSol-gel 1.0021 120° C./ 970° C./ 1-pass 135 16% 1.0091 method 6 hours/ 2hours/ pH of 13.5 N₂ ambience Comparative 15 nm Sol-gel 1.0021 120° C./970° C./ 2-pass 130 16% 1.0078 Example [1] method 6 hours/ 2 hours/ pHof 13.5 N₂ ambience Example [3] 37 nm Sol-gel 0.9993 120° C./ 930° C./None 195 23% 1.0104 method 12 hours/ 2 hours/ pH of 13 N₂ ambienceExample [4] 37 nm Sol-gel 0.9993 120° C./ 930° C./ 1-pass 190 23% 1.0096method 12 hours/ 2 hours/ pH of 13 N₂ ambience Example [5] 37 nm Sol-gel0.9993 120° C./ 930° C./ 2-pass 185 23% 1.0085 method 12 hours/ 2 hours/pH of 13 N₂ ambience Comparative 20 nm Hydrothermal 1.0015 120° C./ 945°C./ None 85 11% 1.0093 Example [2] method 24 hours/ 2 hours/ pH of 13.5N₂ ambience Comparative 20 nm Hydrothermal 1.0015 120° C./ 945° C./1-pass 80 11% 1.0083 Example [3] method 24 hours/ 2 hours/ pH of 13.5 N₂ambience Example [6] 25 nm Solid phase 0.9995 120° C./ 960° C./ None 15019% 1.0101 method 16 hours/ 2 hours/ pH of 13 atmosphere Example [7] 25nm Solid phase 0.9995 120° C./ 960° C./ 1-pass 145 19% 1.0093 method 16hours/ 2 hours/ pH of 13 atmosphere Example [8] 25 nm Solid phase 0.9995120° C./ 960° C./ 2-pass 140 19% 1.0083 method 16 hours/ 2 hours/ pH of13 atmosphere Example [9] 10 nm Sol-gel 1.0026 120° C./ 890° C./ None135 13% 1.0092 method 8 hours/ 6 hours/ pH of 13.5 atmosphere Example[10] 10 nm Sol-gel 1.0026 120° C./ 890° C./ 1-pass 130 13% 1.0080 method8 hours/ 6 hours/ pH of 13.5 atmosphere Comparative 25 nm Hydrothermal0.9996 120° C./ 890° C./ None 105 11% 1.0077 Example [4] method 24hours/ 3 hours/ pH of 13.5 atmosphere Example [11] 10 nm Sol-gel 1.0015110° C./ 900° C./ None 80 13% 1.0090 method 2 hours/ 2 hours/ pH of 13.5N₂ ambience Example [12] 10 nm Sol-gel 1.0015 110° C./ 900° C./ None 9013% 1.0092 method 2 hours/ 2.5 hours/ pH of 13.5 N₂ ambience Example[13] 10 nm Sol-gel 1.0015 110° C./ 900° C./ None 95 14% 1.0095 method 2hours/ 4 hours/ pH of 13.5 N₂ ambience

For example, a comparison of Examples 1 and 2 and Comparative Example 1shows that dry crushing reduces the average particle size of bariumtitanate powder and also reduces the c/a, without affecting thepercentage of twin defects, while a comparison of Examples 11 to 13finds that a longer heat treatment increases the average particle sizeand causes both the percentage of twin defects and c/a to become higher.

Additionally, Comparative Example 4 shows that neither the requiredpercentage of twin defects nor c/a can be achieved, depending on themanufacturing conditions for barium titanate powder.

TABLE 2 Average Variation in capacitance capacitance (σ/X) μF (%)Example [1] 1.08 1.7 Example [2] 1.01 2.0 Comparative 0.98 3.2 Example[1] Example [3] 1.11 1.8 Example [4] 1.12 1.5 Example [5] 1.14 2.3Comparative 0.93 3.5 Example [2] Comparative 0.91 4.5 Example [3]Example [6] 1.03 1.5 Example [7] 1.04 2.1 Example [8] 1.03 2.5 Example[9] 1.02 1.9 Example [10] 1.04 2.1 Comparative 0.97 5.1 Example [4]Example [11] 0.95 2.8 Example [12] 0.95 2.7 Example [13] 0.98 2.7

In the present disclosure where conditions and/or structures are notspecified, a skilled artisan in the art can readily provide suchconditions and/or structures, in view of the present disclosure, as amatter of routine experimentation. Also, in the present disclosureincluding the examples described above, any ranges applied in someembodiments may include or exclude the lower and/or upper endpoints, andany values of variables indicated may refer to precise values orapproximate values and include equivalents, and may refer to average,median, representative, majority, etc. in some embodiments. Further, inthis disclosure, an article “a” or “an” may refer to a species or agenus including multiple species, and “the invention” or “the presentinvention” may refer to at least one of the embodiments or aspectsexplicitly, necessarily, or inherently disclosed herein. In thisdisclosure, any defined meanings do not necessarily exclude ordinary andcustomary meanings in some embodiments.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

I claim:
 1. A multi-layer ceramic capacitor made by alternately layeringa dielectric layer constituted by a sintered body of a ceramic powder,and an internal electrode layer, said ceramic powder containing bariumtitanate powder having a perovskite structure with a median size of 200nm or smaller as measured by SEM observation, wherein the bariumtitanate powder is such that the percentage of barium titanate particleshaving twin defects in the barium titanate powder is 13% or more asmeasured by TEM observation and that its crystal lattice c/a is 1.0080or more.
 2. A multi-layer ceramic capacitor according to claim 1,wherein the median size of the barium titanate powder is 80 to 200 nm.3. A multi-layer ceramic capacitor according to claim 1, wherein thepercentage of barium titanate particles having twin defects in thebarium titanate powder is 13 to 23%.
 4. A multi-layer ceramic capacitoraccording to claim 2, wherein the percentage of barium titanateparticles having twin defects in the barium titanate powder is 13 to23%.
 5. A multi-layer ceramic capacitor according to claim 1, whereinthe crystal lattice c/a of the barium titanate powder is 1.0091 to1.0105.
 6. A multi-layer ceramic capacitor according to claim 2, whereinthe crystal lattice c/a of the barium titanate powder is 1.0091 to1.0105.
 7. A multi-layer ceramic capacitor according to claim 3, whereinthe crystal lattice c/a of the barium titanate powder is 1.0091 to1.0105.
 8. A multi-layer ceramic capacitor according to claim 4, whereinthe crystal lattice c/a of the barium titanate powder is 1.0091 to1.0105.